Effect of Storage Temperatures on the Moisture Migration and Microstructure of Beef

The effects of freezing temperature on the microstructure and moisture migration of beef were investigated, aiming to provide the potential theoretical basis for the beef storage. Drip loss, surface hydrophobicity, and secondary structure of myofibrillar proteins, ice crystal, and micro- and ultrastructure of meat were analyzed at 4°C, −1°C, −6°C, −9°C, −12°C, and −18°C, respectively. Results indicated that the drip loss and surface hydrophobicity of samples stored at −12°C were significantly lower than that stored at 4°C and −1°C (p<0.05) and no significant difference with −18°C (p>0.05). Result from Fourier transform infrared spectroscopy suggested that protein denaturation occurred after storage. There was an increase in α-helices and decline in random coil at lower temperature (−12°C and −18°C). It was indicated that the samples stored at −12°C and −18°C could effectively restrain the denaturation of protein and maintain the stability of secondary structure. The analysis of the ice crystal and micro- and ultrastructure of the muscle indicated that the structure of samples stored at −12°C and −18°C had more integrity and was complete than that stored at 4°C and −1°C. The spaces (water “reservoir” and “channel”) where was the origination of drip were small. Furthermore, the results of low-field nuclear magnetic resonance and 1H magnetic relaxation image showed that the freezing at −12°C could inhibit the migration of immobilized water to free water.

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The Molecular Properties of Peanut Protein: Impact of Temperature, Relative Humidity and Vacuum Packaging during Storage

Molecules ◽

10.3390/molecules23102618 ◽

2018 ◽

Vol 23 (10) ◽

pp. 2618 ◽

Cited By ~ 5

Author(s):

Xiaotong Sun ◽

Hua Jin ◽

Yangyang Li ◽

Haiying Feng ◽

Chunhong Liu ◽

...

Keyword(s):

Secondary Structure ◽

Functional Properties ◽

Surface Hydrophobicity ◽

Protein Isolate ◽

Peanut Protein ◽

Molecular Properties ◽

Random Coil ◽

Bivariate Correlation ◽

Protein Particle ◽

Α Helix

This study aimed to investigate the variation of molecular functional properties of peanut protein isolate (PPI) over the storage process and reveal the correlation between the PPI secondary structure and properties in the storage procedure. After storage, the molecular properties of PPI changed significantly (p < 0.05). Extending storage time resulted in a decrease in free sulfhydryl content, fluorescence intensity, surface hydrophobicity and emulsifying properties, which was accompanied by an increase in protein particle size. The results of infrared spectroscopy suggested the content decline of α-helix and β-sheet, and the content rise of β-turn and random coil. Based on bivariate correlation analysis, it was revealed that surface hydrophobicity and emulsifying activity of PPI was significantly affected by α-helix and by β-turn (p < 0.05), respectively. This research supplied more information for the relationship between the peanut protein’s secondary structure and functional properties over the stored process.

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Effects of High-Pressure Homogenization at Different Pressures on Structure and Functional Properties of Oyster Protein Isolates

International Journal of Food Engineering ◽

10.1515/ijfe-2018-0009 ◽

2018 ◽

Vol 14 (4) ◽

Cited By ~ 5

Author(s):

Cuiping Yu ◽

Fan Wu ◽

Yue Cha ◽

Yuting Qin ◽

Ming Du

Keyword(s):

Particle Size ◽

High Pressure ◽

Secondary Structure ◽

Zeta Potential ◽

Functional Properties ◽

Surface Hydrophobicity ◽

Random Coil ◽

Foaming Properties ◽

High Pressure Homogenization ◽

Protein Profiles

Abstract Oyster protein isolate (OPI) suspensions (6.19 % ± 0.82 %, w/v) were treated by high-pressure homogenization (HPH) at 0 (control), 20, 40, 60, 80 or 100 MPa for three cycles. Protein profiles, secondary structure, free sulfhydryl, surface hydrophobicity, particle size distribution, zeta-potential, solubility, water and oil holding capacity (OHC), emulsifying and foaming properties of the obtained suspensions were analyzed. The results showed that HPH treatment did not cause changes in protein profiles of OPI, but caused changes in secondary structure, content of α-helix decreased but content of β-turn and random coil increased significantly (P < 0.05). Free sulfhydryl and surface hydrophobicity all increased significantly (P < 0.05) after HPH treatment, indicating that tertiary and quaternary structures changed. Functional properties of OPI significantly (P < 0.05) improved after HPH treatment, such as zeta-potential (from −12.67 to −33.57 mV), solubility (from 20.24 % to 57.99 %), OHC (from 981.77 % to 1229.40 %), foaming ability (from 17.50 % to 35.00 %), foaming stability (from 44.49 % to 66.60 %), emulsifying activity index (from 8.87 to 17.06 m2/g) and emulsion stability index (from 14.65 to 41.68 min). At 60 MPa and 80 MPa, the improvements were more remarkable. However, HPH treatment significantly (P < 0.05) decreased particle size (from 200–500 nm to 0–200 nm) and water holding capacity (from 341.15 % to 216.96 %). These improvements were closely related to structural changes and reduction of particle size. Application of different pressures affected functional properties of OPI. These results could provide information for determining HPH applying condition in OPI modification.

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High-Intensity Ultrasound Pulses Effect on Physicochemical and Antioxidant Properties of Tilapia (Oreochromis niloticus) Skin Gelatin

Applied Sciences ◽

10.3390/app10031004 ◽

2020 ◽

Vol 10 (3) ◽

pp. 1004

Author(s):

Dulce Alondra Cuevas-Acuña ◽

Joe Luis Arias-Moscoso ◽

Wilfrido Torres-Arreola ◽

Francisco Cadena-Cadena ◽

Ramón Gertrudis Valdez-Melchor ◽

...

Keyword(s):

Secondary Structure ◽

Oreochromis Niloticus ◽

High Intensity ◽

Antioxidant Properties ◽

Random Coil ◽

Free Radical Scavengers ◽

High Intensity Ultrasound ◽

Reducing Ability ◽

Significant Difference ◽

Ultrasound Pulse

Ultrasonic pulses are considered green technology for the improvement of the functional properties of proteins. In this study, four high-intensity ultrasound pulse treatments (ultrasound-pulsed gelatin (UPG)-42, UPG-52, UPG-71, UPG-84, and non-pulsed control gelatin (CG)) were applied to tilapia (Oreochromis niloticus) skin gelatin in order to study their effect on its physicochemical and antioxidant properties; a non-treated gelatin was used as a control. UPGs showed a significant increase in soluble protein and surface hydrophobicity compared to the control gelatin, and no significant difference was found in the electrophoretic profiles. The effects on the secondary structure were studied by circular dichroism and infrared spectra, and these showed that the random coil conformation was the main component in all treatments and the ultrasonic treatments only affected the α-helix and β-sheet proportion. Finally, the ABTS ((2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid)) and FRAP (ferric reducing ability) assays demonstrated that ultrasound treatments could improve the antioxidant activity of gelatins as free radical scavengers and electron donors. These results suggest that high-intensity ultrasound pulse technology is useful to improve fish gelatin antioxidant properties, which could be associated with secondary structure disruption.

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Effect of Heat Treatment on the Property, Structure, and Aggregation of Skim Milk Proteins

Frontiers in Nutrition ◽

10.3389/fnut.2021.714869 ◽

2021 ◽

Vol 8 ◽

Author(s):

Hongbo Li ◽

Tingting Zhao ◽

Hongjuan Li ◽

Jinghua Yu

Keyword(s):

Secondary Structure ◽

Disulfide Bonds ◽

Polyacrylamide Gel Electrophoresis ◽

Whey Proteins ◽

Skim Milk ◽

Milk Proteins ◽

Surface Hydrophobicity ◽

Random Coil ◽

Heat Treated ◽

Different Temperatures

To study the mechanism of heat-induced protein aggregates, skim milk was heated at 55, 65, 75, 85, and 95°C for 30 s. Then, the sulfhydryl content, surface hydrophobicity, and secondary structure of heat-treated skim milk were studied. Treating skim milk at different temperatures induced a decrease in sulfhydryl content (75.9% at 95°C) and an increase in surface hydrophobicity (44% at 95°C) with a disrupted secondary structure containing random coil, β-sheet, and β-turn of skim milk proteins. The change in these properties facilitated aggregate formation through disulfide bonds and hydrophobicity interaction. Microstructural observation also showed a higher degree of aggregation when skim milk was heated at 85 and 95°C. The result of two-dimensional polyacrylamide gel electrophoresis demonstrated that the aggregates consisted of a high proportion of κ-casein, β-lactoglobulin, and other whey proteins.

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Quality Retention of Fresh Tuna Stored Using Supercooling Technology

Foods ◽

10.3390/foods9101356 ◽

2020 ◽

Vol 9 (10) ◽

pp. 1356

Author(s):

Taiyoung Kang ◽

Timothy Shafel ◽

Dongyoung Lee ◽

Chang Joo Lee ◽

Seung Hyun Lee ◽

...

Keyword(s):

Electric Fields ◽

Electrochemical Impedance ◽

Cell Damage ◽

Cellular Damage ◽

Drip Loss ◽

Ice Crystal ◽

K Value ◽

Microstructure Observation ◽

Quality Retention ◽

Significant Difference

The present study was focused on the investigation of physiochemical changes in tuna subjected to a novel supercooling preservation, which was assisted using a combination of pulsed electric fields (PEF) and oscillating magnetic fields (OMF). Fresh tuna fillets were stored without freezing at −3.2 °C for 8 days. The electrochemical impedance spectroscopy (EIS) parameter Py indicated that there was a significant difference between the frozen-thawed samples (36.3%) and fresh (46.6%) and supercooled (45.9%) samples, indicating that cell damage from ice crystal growth did not occur in the supercooled tuna sample. The microstructure observation and drip loss measurement further confirmed that the ice crystal damage was present in frozen tuna, whereas no cellular damage was found in the supercooled samples. The EIS proved its ability to distinguish between tuna samples that were frozen or chilled (i.e., refrigerated and supercooled) during storage; however, it was less sensitive in detecting the extent of spoilage. Instead, the K-value was used to evaluate tuna freshness, and the measured K-values of the refrigerated, supercooled, and frozen tuna samples after 8 days of storage were 74.3%, 26.4%, and 19.9%, respectively, suggesting that the supercooling treatment significantly preserved the tuna fillets fresh with the improved shelf-life when compared to conventional refrigeration.

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Effect of Temperature and pH on the Secondary Structure and Denaturation Process of Jumbo Squid Hepatopancreas Cathepsin D.

Protein and Peptide Letters ◽

10.2174/0929866526666190405124353 ◽

2019 ◽

Vol 26 (7) ◽

pp. 532-541 ◽

Cited By ~ 1

Author(s):

Cadena-Cadena Francisco ◽

Cárdenas-López José Luis ◽

Ezquerra-Brauer Josafat Marina ◽

Cinco-Moroyoqui Francisco Javier ◽

López-Zavala Alonso Alexis ◽

...

Keyword(s):

Circular Dichroism ◽

Secondary Structure ◽

Cathepsin D ◽

Thermal Denaturation ◽

Protein Denaturation ◽

Marine Organisms ◽

Effect Of Temperature ◽

Jumbo Squid ◽

Α Helix ◽

Circular Dichroïsm

Background: Cathepsin D is a lysosomal enzyme that is found in all organisms acting in protein turnover, in humans it is present in some types of carcinomas, and it has a high activity in Parkinson's disease and a low activity in Alzheimer disease. In marine organisms, most of the research has been limited to corroborate the presence of this enzyme. It is known that cathepsin D of some marine organisms has a low thermostability and that it has the ability to have activity at very acidic pH. Cathepsin D of the Jumbo squid (Dosidicus gigas) hepatopancreas was purified and partially characterized. The secondary structure of these enzymes is highly conserved so the role of temperature and pH in the secondary structure and in protein denaturation is of great importance in the study of enzymes. The secondary structure of cathepsin D from jumbo squid hepatopancreas was determined by means of circular dichroism spectroscopy. Objective: In this article, our purpose was to determine the secondary structure of the enzyme and how it is affected by subjecting it to different temperature and pH conditions. Methods: Circular dichroism technique was used to measure the modifications of the secondary structure of cathepsin D when subjected to different treatments. The methodology consisted in dissecting the hepatopancreas of squid and freeze drying it. Then a crude extract was prepared by mixing 1: 1 hepatopancreas with assay buffer, the purification was in two steps; the first step consisted of using an ultrafiltration membrane with a molecular cut of 50 kDa, and the second step, a pepstatin agarose resin was used to purification the enzyme. Once the enzyme was purified, the purity was corroborated with SDS PAGE electrophoresis, isoelectric point and zymogram. Circular dichroism is carried out by placing the sample with a concentration of 0.125 mg / mL in a 3 mL quartz cell. The results were obtained in mdeg (millidegrees) and transformed to mean ellipticity per residue, using 111 g/mol molecular weight/residue as average. Secondary-structure estimation from the far-UV CD spectra was calculated using K2D Dichroweb software. Results: It was found that α helix decreases at temperatures above 50 °C and above pH 4. Heating the enzyme above 70°C maintains a low percentage of α helix and increases β sheet. Far-UV CD measurements of cathepsin D showed irreversible thermal denaturation. The process was strongly dependent on the heating rate, accompanied by a process of oligomerization of the protein that appears when the sample is heated, and maintained a certain time at this temperature. An amount typically between 3 and 4% α helix of their secondary structure remains unchanged. It is consistent with an unfolding process kinetically controlled due to the presence of an irreversible reaction. The secondary structure depends on pH, and a pH above 4 causes α helix structures to be modified. Conclusion: In conclusion, cathepsin D from jumbo squid hepatopancreas showed retaining up to 4% α helix at 80°C. The thermal denaturation of cathepsin D at pH 3.5 is under kinetic control and follows an irreversible model.

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A method for validating the accuracy of NMR protein structures

Nature Communications ◽

10.1038/s41467-020-20177-1 ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

Nicholas J. Fowler ◽

Adnan Sljoka ◽

Mike P. Williamson

Keyword(s):

Secondary Structure ◽

Crystal Structures ◽

Protein Structures ◽

Random Coil ◽

Local Rigidity ◽

Correlation Score ◽

Nmr Structures ◽

Explicit Solvent ◽

Structure Ensemble ◽

Better Than

AbstractWe present a method that measures the accuracy of NMR protein structures. It compares random coil index [RCI] against local rigidity predicted by mathematical rigidity theory, calculated from NMR structures [FIRST], using a correlation score (which assesses secondary structure), and an RMSD score (which measures overall rigidity). We test its performance using: structures refined in explicit solvent, which are much better than unrefined structures; decoy structures generated for 89 NMR structures; and conventional predictors of accuracy such as number of restraints per residue, restraint violations, energy of structure, ensemble RMSD, Ramachandran distribution, and clashscore. Restraint violations and RMSD are poor measures of accuracy. Comparisons of NMR to crystal structures show that secondary structure is equally accurate, but crystal structures are typically too rigid in loops, whereas NMR structures are typically too floppy overall. We show that the method is a useful addition to existing measures of accuracy.

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Effects of in-Office and at-Home Bleaching on Human Enamel and Dentin: An in vitro Application of Fourier Transform Infrared Study

Applied Spectroscopy ◽

10.1366/000370208786401554 ◽

2008 ◽

Vol 62 (11) ◽

pp. 1274-1279 ◽

Cited By ~ 19

Author(s):

Feride Severcan ◽

Kurtulus Gokduman ◽

Ayca Dogan ◽

Sukran Bolay ◽

Saadet Gokalp

Keyword(s):

Fourier Transform ◽

Structural Changes ◽

Protein Denaturation ◽

Random Coil ◽

Protein Ratio ◽

Band Frequency ◽

Human Enamel ◽

Ft Ir ◽

At Home

In-office and at-home bleaching techniques are widely used methods for the whitening of teeth. However, the safety of these techniques has not been clarified yet. The aim of the current study is to investigate the in-office- and at-home-bleaching-induced structural and quantitative changes in human enamel and dentin at the molecular level, under in vitro conditions. The Fourier transform mid-infrared (mid-FT-IR) spectroscopic technique was used to monitor bleaching-induced structural changes. Band frequency and intensity values of major absorptions such as amide A, amide I, phosphate (PO4), and carbonate (CO3−2) bands, for treatment groups and control, were measured and compared. The results revealed that both procedures have negligible effects on dentin constituents. In office-bleached enamel, in addition to demineralization, a decrease in protein and polysaccharide concentrations, mineral-to-protein ratio, and the strength of hydrogen bonds around NH groups, as well as a change in protein secondary structure were observed. The protein structure changed from β-sheet to random coil, which is an indication of protein denaturation. However, no significant variations were observed for at-home bleached enamel. The control, at-home, and in-office bleached enamel samples were differentiated with a high accuracy using cluster analysis based on FT-IR data. This study revealed that office bleaching caused deleterious alterations in the composition and structure of enamel that significantly affected the crystallinity and mineralization of the tissue. Therefore, at-home bleaching seems to be much safer than in-office bleaching in terms of molecular variations.

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Characterization of porcine osteonectin extracted from foetal calvariae

Biochemical Journal ◽

10.1042/bj2530139 ◽

1988 ◽

Vol 253 (1) ◽

pp. 139-151 ◽

Cited By ~ 69

Author(s):

C Domenicucci ◽

H A Goldberg ◽

T Hofmann ◽

D Isenman ◽

S Wasi ◽

...

Keyword(s):

Amino Acids ◽

Secondary Structure ◽

Type I Collagen ◽

Culture Shock ◽

Gel Filtration ◽

Alpha Helix ◽

Type I ◽

Homologous Proteins ◽

Compact Structure ◽

Significant Difference

Osteonectin, extracted from foetal porcine calvariae with 0.5 M-EDTA, was purified to homogeneity by using gel filtration and polyanion anion-exchange fast protein liquid chromatography under dissociative conditions without the need of reducing agents. The purified protein migrated with an Mr of 40,300 on SDS/polyacrylamide gels and was similar to bovine osteonectin in both amino acid composition and in its ability to bind to hydroxyapatite in the presence of 4 M-guanidinium hydrochloride (GdmCl). However, unlike the bovine protein, porcine osteonectin did not bind selectively to hydroxyapatite when EDTA tissue extracts were used. In addition, purified porcine osteonectin did not show any apparent affinity for either native or denatured type I collagen, but did bind to serum albumin. Primary sequence analysis revealed an N-terminal alanine residue, with approximately one-half of the subsequent 35 residues identified as small hydrophobic amino acids and one-quarter as acidic amino acids. The only significant difference between the N-terminal sequences of the bovine and porcine proteins was the deletion of the tripeptide Val-Ala-Glu in porcine osteonectin. In contrast with bovine osteonectin, far-u.v.c.d. of porcine osteonectin revealed considerable secondary structure, of which 27% was alpha-helix and 39% was beta-sheet. Cleavage of the molecule with CNBr under non-reducing conditions generated five fragments, of which two major fragments (Mr 27,900 and 12,400) stained blue with Stains All, a reagent that stains sialic-acid-rich proteins/phosphate-containing proteins and/or Ca2+-binding proteins blue while staining other proteins pink. The 12,400-Mr fragment bound 45Ca2+ selectively, indicating a Ca2+-binding site in this part of the molecule. The 27,900-Mr fragment did not bind Ca2+, and since biosynthetic studies with 32PO4(3-) did not show phosphorylation of porcine osteonectin, this fragment is likely to be highly acidic. The incomplete cleavage of the molecule with CNBr and the ability of the molecule to regain its secondary structure after exposure to 7 M-urea are features consistent with the molecule having a compact structure that is stabilized by numerous disulphide bridges. The chemical and binding properties of porcine osteonectin are closely similar to the recently described ‘culture shock’, SPARC and BM-40 proteins, indicating that these are homologous proteins.

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Epiplasts: Membrane Skeletons and Epiplastin Proteins in Euglenids, Glaucophytes, Cryptophytes, Ciliates, Dinoflagellates, and Apicomplexans

mBio ◽

10.1128/mbio.02020-18 ◽

2018 ◽

Vol 9 (5) ◽

Cited By ~ 6

Author(s):

Ursula Goodenough ◽

Robyn Roth ◽

Thamali Kariyawasam ◽

Amelia He ◽

Jae-Hyeok Lee

Keyword(s):

Electron Microscopy ◽

Plasma Membrane ◽

Amino Acid ◽

Secondary Structure ◽

Amino Acid Composition ◽

Acid Composition ◽

Random Coil ◽

Cell Cortex ◽

Tail Domain ◽

Membrane Skeletons

ABSTRACTAnimals and amoebae assemble actin/spectrin-based plasma membrane skeletons, forming what is often called the cell cortex, whereas euglenids and alveolates (ciliates, dinoflagellates, and apicomplexans) have been shown to assemble a thin, viscoelastic, actin/spectrin-free membrane skeleton, here called the epiplast. Epiplasts include a class of proteins, here called the epiplastins, with a head/medial/tail domain organization, whose medial domains have been characterized in previous studies by their low-complexity amino acid composition. We have identified two additional features of the medial domains: a strong enrichment of acid/base amino acid dyads and a predicted β-strand/random coil secondary structure. These features have served to identify members in two additional unicellular eukaryotic radiations—the glaucophytes and cryptophytes—as well as additional members in the alveolates and euglenids. We have analyzed the amino acid composition and domain structure of 219 epiplastin sequences and have used quick-freeze deep-etch electron microscopy to visualize the epiplasts of glaucophytes and cryptophytes. We define epiplastins as proteins encoded in organisms that assemble epiplasts, but epiplastin-like proteins, of unknown function, are also encoded in Insecta, Basidiomycetes, andCaulobactergenomes. We discuss the diverse cellular traits that are supported by epiplasts and propose evolutionary scenarios that are consonant with their distribution in extant eukaryotes.IMPORTANCEMembrane skeletons associate with the inner surface of the plasma membrane to provide support for the fragile lipid bilayer and an elastic framework for the cell itself. Several radiations, including animals, organize such skeletons using actin/spectrin proteins, but four major radiations of eukaryotic unicellular organisms, including disease-causing parasites such asPlasmodium, have been known to construct an alternative and essential skeleton (the epiplast) using a class of proteins that we term epiplastins. We have identified epiplastins in two additional radiations and present images of their epiplasts using electron microscopy. We analyze the sequences and secondary structure of 219 epiplastins and present an in-depth overview and analysis of their known and posited roles in cellular organization and parasite infection. An understanding of epiplast assembly may suggest therapeutic approaches to combat infectious agents such asPlasmodiumas well as approaches to the engineering of useful viscoelastic biofilms.

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